The invention concerns a cooling container for the cooling with liquid, especially of oil, of a semiconductor construction element which is thermically and electrically pressure-contacted with one with its container floors as well as a process for manufacturing such a container.
The cooling container is used for semiconductor (power) construction elements in disk cell construction with power losses in the order of several hundred watts and more with two-sided heat flow. For this purpose, in a generally known manner, cooling containers, through which the liquid passes, are by means of a tension device connected to the two main surfaces of the disk cell and are optionally held together in piles and/or coupled with each other by means of a liquid-transporting supporting rail. The semiconductor construction elements which are cooled in this manner can be used in rectifier facilities for the high tension direct current transmission (HGU), in electric locomotives or other fields of application.
Semiconductor construction elements which in regard to current are subjected to higher loads require coolers for the flow of their power loss. According to construction and setup, these semiconductor construction elements are unable to perform this task. The permissible power loss is represented by the quotient of the temperature gradients and the thermic resistance. The temperature gradient is formed as the difference of the permissible crystal temperature of the semiconductor element and the highest cooling temperature. The thermic resistance is a result of the semiconductor, the transition between it and the cooler and the latter itself (F. Korb, "Thermic Behavior of Power Semiconductors", Special Edition from "Industrial Electrical Engineering & Electronics," Year 20, Volume 19 and 21, 1975 = BBC Print D IA 60037 D). Since the two first terms of the total thermic resistance are specific to construction elements, only the decrease of the cooler resistance can result in an increase of the power loss and thus the current intensity.
The thermic resistance of a cooler consists of line resistance and transfer resistance, in which case the latter occurs because of the conditions of the transition of the heat to the cooling medium. The transfer resistance is inversely proportional to the product of heat-emitting surface and the coefficient of heat transfer. If this value is determined by the rate of the speed of the cooling agent and the surface structure, the heat-emitting surface must be increased in order to decrease the transfer resistance. However, this results in the fact that the total heat conduction resistance will increase. The result for metallic air coolers is a law of growth for weights and/or volume with an exponent of the power of &gt;3.
In the case of the known cooling by means of heat ducts (Korb, above, M. Groll and B. Zimmermann, "Heat and Material Transfer," Vol 4, (1971), Page 39 to 47), the line resistance is reduced by the fact that one uses water vapor for transporting the heat over a certain distance. An air cooler is attached to the closed end of the heat duct. The condensate is led back through capillary tubes, networks or arteries. In the case of power losses in the order of 800 W -- disk cell with two-sided heat flow -- one can, in this case, reduce weight and volume to approximately 40% of a customary aluminum cooler.
If there are requirements for smaller weights and volumes, one must work with vapor or passing liquid as heat conveying means. Because of the significantly better coefficients of heat transfer of liquids as compared to air, one may get along with much smaller heat-emitting surfaces and thus with considerably reduced heat paths.
The most favorable coefficients of heat transfer for a noncirculating water cooling are furnished by water; they are one thousand times better than those furnished by air, referred to equal flow speeds and temperatures. However, water, because of operational conditions, for example, discontinuous operation, frost, inability to heat, cannot always be used and also requires longer hydraulic connecting lines in order to obtain a corresponding insulation level and, for its maintenance, an ion exchanger. In such cases, transformer oil, an insulating cooling agent which has proven itself in electronics, offers a solution. However, the heat transfer coefficient of transformer oil is only seventy times better than that of air, i.e., seventeen times worse than in the case of water.